linux-kernel - Re: [PATCH v1 2/5] dt-bindings: soc: hpe: Add hpe,gxp-plreg

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Date:   Sat, 22 Oct 2022 11:52:00 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Hawkins, Nick" <nick.hawkins@....com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     "Verdun, Jean-Marie" <verdun@....com>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v1 2/5] dt-bindings: soc: hpe: Add hpe,gxp-plreg

On 12/10/2022 15:56, Hawkins, Nick wrote:
>>> +examples:
>>> +  - |
>>> +    cpld@...89000 {
>>> +      compatible = "hpe,gxp-plreg", "simple-mfd", "syscon";
>>> +      reg = <0x1e789000 0x1000>;
>>> +      fan1 {
>>> +        bit = <0x01>;
>>> +        inst = <0x27>;
>>> +        id = <0x2B>;
> 
>> These property names are way too generic for device specific properties. There is zero description of what the h/w does and any of these child nodes to give any advice on direction. However, a node per register or register field is generally the wrong direction.
> 
> Thank you for your valued feedback. The goal I was trying to achieve here was making our programmable logic register driver interface in a generic way across multiple platforms based on inputs we provide with the .dts file for each platform. For instance if we want to read the fan 1 install status on platform X it would be reading bit 0x01 of byte 0x27 where as on platform Y it could be bit 0x02 of byte 0x16. Is there a format you would recommend that I can adhere too?

I don't think DT place is to describe register or memory layout, with
some exceptions like MTD partitions or nvmem cells. Basically you are
representing here a device register map inside DT, just because it is a
CPLD.

Every regular multi-functional device handles its register map in the
driver itself and uses Linux framework to expose the internals. CPLD
should not be different, except that is programmable.

Best regards,
Krzysztof